1. Field
At least one example embodiment relates to methods of driving a hybrid inkjet printing apparatus that ejects relatively minute droplets (for example, droplets having a volume of less than about 50 femtoliters), the methods including a piezoelectric method and an electrostatic method.
2. Description of the Related Art
Inkjet printing apparatuses print a desired (or alternatively, predetermined) color image on a surface of a printing sheet by ejecting minute droplets of printing ink onto a desired area of the printing sheet using an inkjet head. Recently, inkjet printing apparatuses have been used in various fields such as flat display fields, for example, liquid crystal displays (LCDs) and organic light emitting devices (OLEDs); flexible display fields, for example, E-paper; printed electronics fields, for example, metal wirings, organic thin film transistors (OTFTs); and the like. When inkjet printing apparatuses are used in the fields of displays or printed electronics, one important technical objective for process technologies is high-resolution and precise printing.
Inkjet printing apparatuses use various inkjet ejecting methods, for example, a piezoelectric method or an electrostatic method. The piezoelectric method is a method of ejecting ink by deforming a piezoelectric element. The electrostatic method is a method of ejecting ink using an electrostatic force. The electrostatic method ejects ink using electrostatic induction, which includes accumulating charged pigments using an electrostatic force and then ejecting ink droplets.
Since a piezoelectric-type printing inkjet printing apparatus ejects ink by using a drop on demand (DOD) method, printing operations of the piezoelectric-type printing inkjet printing apparatus are easily controlled. Further, piezoelectric-type printing inkjet printing apparatuses use a simple driving method, and ejection energy is generated by mechanically deforming a piezoelectric element. Thus, a piezoelectric-type printing inkjet printing apparatus may use any ink. However, the piezoelectric-type printing inkjet printing apparatus has difficulty ejecting ink in minute droplets of several picoliters or less. The piezoelectric-type printing inkjet apparatus also has difficulty with applications requiring relatively high-precision printing.
An electrostatic-type inkjet printing apparatus has been used to address some of the above issues. Electrostatic-type printing apparatuses have a simple driving method, and are capable of ejecting minute ink droplets with a relative precision. However, an electrostatic-induction inkjet printing apparatus of the electrostatic-type inkjet printing apparatus has difficulty in forming separate inkjet paths. Thus, it is difficult to eject ink using a DOD method from a plurality of nozzles. In addition, electrostatic printing methods are limited in ejection speed of ink as well as the kinds of ink used because electrostatic methods require charged pigments with high densities.
With regard to inkjet printing apparatuses in general, the size of ejected ink droplets is proportional to a diameter of a nozzle. Thus, in order to eject minute ink droplets, the size of a nozzle needs to be reduced. However, when the size of the nozzle is reduced, it is difficult to obtain precise nozzles and the nozzle is more likely to clog, thereby reducing reliability.